The beam quality, or brightness, of high power diode laser arrays is generally very poor, and thus inadequate for many applications. A simple approach to improving the output from such an array is to couple each element of the array into a corresponding fiber in a linear fiber array. The output end of the fiber array can be arranged, as desired, for example into a circular bundle. While this approach improves the beam quality in the slow axis, it reduces the beam quality in the fast axis. Further improvement in beam quality can be achieved by interposing coupling optics between the diode laser array and the fiber array.
U.S. Pat. No. 5,127,068 discloses using a small diameter multimode optical fiber as the coupling optics between a diode laser and a butt coupled optical fiber, the optical fiber selected for the coupling optics having a diameter approximately equivalent to the diameter of the fiber to be coupled to the diode laser, and approximately 20% to 50% larger than the lateral dimension of the diode laser of the diode array. Additionally the patent discloses that the selected optical coupling fiber should have a low numerical aperture in order to collimate the high numerical aperture direction of the diode laser emission.
U.S. Pat. No. 5,436,990, a continuation-in-part of U.S. Pat. No. 5,127,068, discloses a system for coupling the output from a diode laser bar into an optical fiber bundle. The mounting system includes means for mounting the coupling optic, consisting of a small diameter multimode optical fiber, to the diode laser bar in a thermally stable configuration.
U.S. Pat. No. 5,949,932 discloses an assembly for focusing and coupling the output of a semiconductor laser into an optical fiber, the assembly including a cylindrical lens interposed between the output surface of the laser and the input surface of the optical fiber. The diameter of the disclosed cylindrical lens is on the order of the core diameter of the optical fiber and, in a preferred embodiment, is comprised of a glass fiber lens glued, fused, or melted onto the input surface of the optical fiber. The cylindrical lens is oriented substantially at a right angle to the optical fiber. In an alternate configuration utilizing a fiber array rather than a single optical fiber, the cylindrical lens is comprised of multiple individual cylindrical lens assemblies which correspond to the number and arrangement of the individual fibers of the array. In this configuration, each individual cylindrical lens is bonded onto the input surface of a corresponding optical fiber.
A variety of optical systems have been designed to couple the output of a diode laser array into an optical fiber or fiber array, these systems utilizing one or more cylindrical lenses. In order to achieve a stable output from the system, both in terms of output spectrum and power, it is critical that the cylindrical lens does not scatter or reflect the emissions of the diode laser back into the diode. As a result of this constraint, the cylindrical lens is coated with an anti-reflection (AR) coating to reduce reflections. Additionally, the cylindrical lens is typically tilted off-angle to further reduce feedback. Unfortunately alignment of the AR coated surfaces as well as properly positioning the cylindrical lens is a time consuming process. Accordingly, what is needed in the art is a means for efficiently coupling the output from a diode laser array into an optical fiber or fiber array, the coupling means being relatively easy to position. The present invention provides such a coupling means.